There are many industrial applications where it is necessary to separate first and second liquids. One application is in separating a small quantity of oil that is intimately mixed with water, so the oil can be recovered for use and the water can be disposed of without violating environmental regulations. A corresponding use is in separating a small amount of water contained in a larger quantity of oil, so the water does not harm machinery that uses the oil. Still another widespread use is in removing light organic components (e.g. kerosene) from an aqueous stream (e.g. water, or electrolyte, or raffinate) as described in U.S. Pat. No. 5,273,654. Larger droplets of the second liquid can be removed by known coalescing devices such as a plate coalescer. However, a high proportion of microscopic droplets, left after coalescing, cannot be removed by such devices.
A high proportion of microscopic droplets of one liquid, such as water mixed into oil, usually can be removed by pumping the mixture through a disposable filter such as an automobile oil filter. However, it is expensive to use such disposable filter where a large quantity of the second liquid must be removed. Perhaps 90% of microscopic droplets would eventually coalesce and rise to the surface of a settling tank, after a period of time of a few days to a few months (assuming the mixture was not disturbed), but this period is too long for most applications. It is noted that automobile filters, fine steel wool, and sintered metal can serve as filters, but they have long passages that clog and that are not readily cleaned by reverse flow. Such devices can be cleaned of oil and a small amount of solid particles by flowing a light hydrocarbon such as kerosene that dissolve them, but this results in the problem of how to environmentally dispose of the kerosene. A system for use in removing a high percentage of microscopic droplets of a second liquid contained in an intimate mixture with a first liquid, such as oil from water, water from oil, or organics from an aqueous stream, which was of moderate cost to construct and operate, would be of value.